(i) Field of the Invention
This invention relates to a variable speed ratio drive mechanism of the kind comprising a pair of friction members mounted for rotation about respective axes of rotation, said friction members presenting opposed friction surfaces at facing ends thereof, said surfaces both frictionally engaging, at respective points of contact thereon, a spherical ball located between the surfaces whereby, when the points of contact are spaced away from the respective axes, rotary motion of one friction member can be transmitted to the other via said ball, and means being provided for altering the distance of at least one of the points of contact from the axis of its associated friction member whereby to vary the drive ratio between said members; said surfaces being concave and formed as surfaces of revolution defined about the axes of respective friction members, the radii of curvature of the respective surfaces being everywhere greater than the radius of curvature of the ball and said ball being maintained captured between said surfaces.
(II) Description of the Prior Art
French Pat. No. 815,862, for example, discloses a mechanism of the above kind in which ratio changing is effected by moving the said one friction member, this member being carried by a shaft mounted in bearings which are themselves pivotal relative to the other friction member. The coupling of input and output shafts to the mechanism is thus complicated and one object of the invention is to provide an improved mechanism of the above kind in which this difficulty is lessened. The mechanism of French Pat. No. 815,862 is also such that the point of contact of the ball with one of the friction surfaces remains substantially constantly spaced from the axis of the associated friction member, thus accentuating wear at this point. Furthermore, the range of available ratios is correspondingly less than if the points of contact at both friction surfaces are variable.